The field of this invention relates to selective locking systems for telescoping joints in offshore riser systems.
Riser systems are used in offshore systems to connect surface equipment to the BOP stack mounted subsea on the wellhead. The telescoping joint compensates for movement of the surface equipment due to wave action. Conditions arise when the telescoping joint needs to be in a locked position. One such situation can occur during times of bad weather when the riser is disconnected from the BOP stack and is freely suspended above the BOP stack. Other operating conditions may dictate that when the telescoping joint strokes to its retracted position that it be automatically locked. Other situations may arise where the telescoping joint needs to be locked in its retracted position where its overall length is the shortest. These situations occur when the joint is being transported or stored.
In the past, when it has been desirable to lock the telescoping joint of a riser system, a manual operation was required. Thus, bolts having eccentric lugs on one part of the joint would have to be turned with tools to orient the eccentrically mounted lug into a groove on another part of the joint so as to hold the telescoping joint in a retracted position. Dual packer assemblies made by Cooper Cameron Corporation included this feature. The problem with doing this was that the riser system is in a relatively inaccessible area known as the xe2x80x9cmoonpoolxe2x80x9d of the surface rig. Thus, operating personnel had to be hoisted to obtain access to the various bolts and try to rotate them while suspended adjacent to them in a sling. This procedure was difficult to accomplish and involved certain risks from a safety standpoint.
Different types of connections for other applications involving hydraulic assist for make-up have been used. Cooper Cameron makes an HC collet connector which employs hydraulic cylinders moving a sleeve to cam a grooved collet to catch a groove on the collet around mating flange connections of a joint to hold the joint together. Other connectors are illustrated in U.S. Pat. Nos. 4,348,039; 4,372,584; 4,632,432; 4,854,777; 5,163,783; 5,462,121; 5,692,564; 5,718,291.
What these connections lack is a simple design which can support extremely high loads and be adjusted easily for different modes of operation. The prior designs, specific to the application of telescoping joints for risers, involved manual operations which were time-consuming and presented risks to personnel. Thus, one of the objects of the present invention is to provide a simple system which can accommodate a variety of situations without the need of close access to the telescoping joint by personnel within the moon-pool. Another objective of the present invention is to provide a design which will accommodate the high loads required, while at the same time be easily positionable in multiple positions where either normal operations can take place, or the telescoping joint is locked in a retracted position, or that the telescoping joint locks if it reaches a fully retracted position during normal operations.
These and other advantages will become apparent to those skilled in the art from a review of the preferred embodiment described below.
An automatic locking mechanism for a telescoping joint for a riser functions in several modes. In an operating mode, the joint is free to have its inner and outer barrels move with respect to each other without engaging each other in a locking relationship. In a second position, the telescoping joint locks when it is fully retracted. In a third position, the system locks the inner and outer barrels together to hold them in a fixed position. The inner and outer barrels are locked when a movable sleeve is properly positioned to allow spring-loaded dogs to be biased through windows in the sleeve so as to act as a landing shoulder to catch a groove on the outer barrel. By putting the actuating sleeve in a variety of positions, the various modes of the locking assembly can be deployed.